1. Field of the Invention
The invention relates to manhole cover supports and, in particular, to a separate ring placed within an existing manhole frame to raise the height of the manhole cover to compensate for added roadway pavement. More particularly, the invention relates to an improved method for installing the ring in the manhole frame.
2. Description of the Prior Art
Most underground facilities such as sanitary and storm sewers, utility conduits and the like have manhole openings to provide access thereto. These manholes usually are located in the street or roadway and consist of an inverted bell-shaped metal frame mounted on top of a brick or concrete base structure. This metal frame has an internal ledge for supporting the manhole cover so that the top of the cover is level with the top of the frame and surrounding roadway pavement.
Problems arise quite frequently in the resurfacing of roadways in that a layer of pavement is placed on the existing pavement, resulting in the manhole cover being below the top surface of the new pavement causing a depression in the roadway. It is quite difficult and expensive to raise the existing manhole frame sufficiently to compensate for the added pavement.
Various devices and methods have been constructed and used which enable an existing manhole cover to be raised to the level of the new pavement surface without raising the existing manhole frame. Examples of these devices and methods are shown in U.S. Pat. Nos. 1,517,871, 3,218,943, 3,773,428, and 3,891,337.
Some of these prior art devices, although apparently providing the desired results, are expensive to manufacture due to the number of machining and forming operations required for their fabrication. Likewise, these devices achieve their adjustment and/or clamping engagement with the manhole frame by a threaded screw mechanism or inclined, frictionally retained wedge which in time may become loose due to the continuous vibration caused by passing vehicles. These screw mechanisms and wedges become corroded, preventing removal of the elevating ring should their removal be required in the future. Also, most known devices use an expanding mechanism which protrudes into the I.D. of the manhole, thereby reducing the actual I.D. as well as creating a work and safety hazard for workmen climbing into and out of the manhole opening.
Many of the problems encountered with these known constructions and devices are believed to be overcome by the manhole cover support ring shown in my earlier U.S. Pat. No. 4,097,171. Use of the manhole cover elevating and support ring of U.S. Pat. No. 4,097,171 in actual field installations indicates that the construction is performing quite satisfactorily.
However, it is important for nearly all manufacturers to be able to provide their products at as low a cost as possible without sacrificing quality. The present invention provides an elevating ring construction and a method of installing the same in a manhole frame which reduces the cost of my previously patented support ring while providing the same satisfactory results. This reduction in cost is achieved by eliminating the toggle mechanism and the mounting of this mechanism on the elevating ring so it functions as an integral part of the ring construction. Cost reduction also is achieved during installation by eliminating some of the operations which may be required to be performed on the ring in the field by the workmen.
No known manhole cover elevating and support ring and method of installing the same of which I am aware uses the natural elasticity in a compressed split metal ring to clamp the ring within the manhole cover frame, or uses a separate adjustable link that is force-fitted within a gap formed in the split ring, alone or in combination with the elasticity of the compressed ring, to clamp the ring in the frame opening.